Industrial design is driving demand for shaped cover glass for portable electronic devices such as smart phones and tablets. A typical shaped cover glass of interest has a combination of a large flat section for covering the front side of the electronic device and one or more curved sections for wrapping around one or more edges of the electronic device. The curved sections include bends and corners where they intersect with the flat sections. A flat electronic device will require a small bend radius, e.g., less than 20 mm, to allow the curved section to wrap around an edge of the device while maintaining the flat appearance of the device.
Shaped glass articles with small radius bends and corners are difficult and expensive to make using glass machining. Glass machining involves large material removal, which greatly increases cost. Total removal of machining marks with polishing is difficult to impossible. It is also very difficult to achieve an even polish on curved sections without inducing optical distortions in the glass article.
Thermal reforming with molds can avoid some of the challenges inherent in glass machining. However, there are also challenges with precision forming of small radius bends and corners with this approach, especially when the glass has a high softening point and requires relatively high temperatures to form the bends and corners. At high forming temperatures, interaction between the glass and mold becomes a concern.